When the Tanzanian schoolboy Erasto Mpemba asked a visiting lecturer why hot water freezes faster than cold, he could not have guessed that his observation – made while making ice-cream – would draw the attention of some of the world’s greatest physicists. The phenomenon is now known as the Mpemba effect, but variants of it have baffled philosophers and physicists since the days of Aristotle, and it has subsequently been observed in other contexts, including magnetic systems that display colossal magnetoresistance and colloidal beads falling through the path of optical tweezers.

A trio of researchers in Japan has now added to this list by demonstrating the Mpemba effect theoretically in a simple quantum system. The result may point towards ways of making quantum computers more efficient, though team member Hisao Hayakawa cautions that it is early days. “So far, we don’t have so many experiments on the quantum Mpemba effect,” he tells Physics World.

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